The present invention relates to the field of rocket engine propulsion chambers and to fabricating them.
More particularly, the present invention relates to combustion chambers having a metal inside wall, an outside covering, and a cooling circuit. Typically, such combustion chambers are used in rocket engines using liquid propellants and a regenerative feed circuit, with at least one of the propellants then passing through the cooling circuit of the combustion chamber in order to cool its inside wall while being heated prior to being injected into the combustion chamber. The metal inside wall ensures heat transmission from the inside of the combustion chamber to the cooling circuit.
Normally, the outside covering represents the main structural element of such a combustion chamber. In particular, it takes up the pressure forces from the inside of the combustion chamber, and also the thrust generated by the rocket engine, and various dynamic forces to which the rocket engine is subjected in operation.
In the state of the art, known combustion chambers usually have an outside covering that is likewise made of metal, and in particular of nickel. Nevertheless, such a metal outside covering normally presents a large coefficient of thermal expansion, thereby leading to large thermomechanical stresses between the relatively cold covering and the relatively hot inside wall, which stresses are particularly great when a cryogenic propellant, such as liquid hydrogen, passes through the cooling circuit of the combustion chamber. Furthermore, the hydrogen may also have harmful effects on the mechanical connections of the outside covering with the inside wall and with other elements made of metal.
In order to solve these problems, and also in order to reduce the cost and the time required for fabricating the combustion chamber, proposals have been made to use organic matrix composite materials in the outside covering. Such organic materials present the advantage of providing thermomechanical properties that are better adapted to the stresses to which the outside covering of the combustion chamber is subjected, while being lighter in weight and better at withstanding hydrogen contamination, and also having a coefficient of thermal expansion that is relatively small. Nevertheless, it is difficult to provide a good mechanical connection between such materials and elements made of metal such as the inside wall. Metal connections have been proposed, but their weight nevertheless negates a large amount of the advantage due to the lightness of the outside covering made of organic matrix composite material.